Flexible optical waveguides for backplane optical interconnections

ABSTRACT

A flexible optical connector suitable for use in an optical backplane for interconnecting optical circuit boards, and methods of making the optical connector, are disclosed. The flexible optical connector comprises a plurality of waveguides on two or more levels providing a plurality of light paths that allow light communication between optical circuit boards. The optical connector can be manufactured separately from the backplane and thereafter mounted on the backplane. The backplane of the present invention may also have a mounting structure for removably retaining and positioning optical circuit board and may, optionally, include electrical traces for providing electrical interconnections between the circuit boards.

FIELD OF THE INVENTION

This invention is related to connecting optical devices. In particular,the present invention is directed to a flexible optical connector, andmethods of manufacturing a flexible optical connector, the opticalconnector being particularly useful for interconnecting optical circuitboards on an optical backplane.

BACKGROUND OF THE INVENTION

The growth of networks capable of handling high data-rate transfer ofvoice and data has increased the demand and performance requirements foroptical networks. While information can be transferred optically overlarge distances, there is generally a need for changing optical signalsto electrical signals and vice versa, requiring structures and devicesfor interfacing the optical components with electrical andelectro-optical components. Thus for example, optical networks includeamplifiers for strengthening optical beams, switches for routingsignals, and converters for transducing, as necessary, electrical andoptical signals at either end of the network. These functions areperformed by devices that include optical, electro-optical andelectrical components.

It is advantageous to use a common backplane to interconnect optical andelectro-optical components on two or more circuit boards. Such circuitboards may be designed for optical communications via the edge of theboards and may, therefore, include one or more edge-mountedelectro-optic devices or edge-terminating optical waveguides. Examplesof optical circuit boards are described in co-owned U.S. Pat. No.6,611,635 to Yoshimura et al., incorporated herein by reference. Onerequirement of a backplane for optical interconnecting between opticalcircuit boards is the need to provide for complex signal routing.

SUMMARY OF THE INVENTION

The present invention provides optical interconnect structures andmethods for providing optical interconnections between optical circuitboards.

In one aspect, the present invention comprises a flexible opticalconnector suitable for use as an optical backplane for communicatingoptical signals between a plurality of optical circuit boards. Theoptical connector includes a flexible strip having a plurality ofwaveguides formed in a plurality of waveguide layers for providing aplurality of optical paths between opposing ends of the flexible strip,where at least one of the optical paths runs through at least two of thewaveguide layers. The optical paths may include input and output portsnear the ends of the flexible strip. The flexible strip may include atleast one pass-through structure for routing light between layers. Thepass-through structure, or optical via, may be used to cause the opticalpaths in the flexible strip to cross over, enabling complex routing ofoptical signals between the optical circuit boards. The pass-throughstructure may comprise a complementary pair of reflective angledsurfaces, and the overall thickness of the strip is, preferably, betweenabout 50 to about 1,000 μm.

The inventive flexible strip may be mounted on a backplane substrate tocouple a plurality of optical circuit boards removably retained andpositioned on the backplane by a mounting structure, such as brackets.The backplane may also provide electrical traces for providingelectrical interconnections between the circuit boards.

In another aspect, the present invention comprises an optical backplanefor communicating optical signals between a plurality of optical circuitboards and optically connect one or more optically active areas of theoptical circuit boards. The optical backplane includes a substrate,mounting structures, such as brackets, for retaining the optical circuitboards, and a plurality of waveguides mounted on the substrate havingwaveguide ends adjacent to the optical circuit boards. The waveguidesare preferably formed in a flexible strip that includes a plurality ofwaveguide layers and a cladding layer separating adjoining ones of theplurality of waveguide layers.

A further aspect of the present invention comprises a method of formingan optical backplane to optically connect an optical circuit boardhaving an edge comprising two or more optically active areas. The methodincludes forming a flexible strip comprising at least two waveguidelayers and having a plurality of waveguides formed therein, saidwaveguides having waveguide ends, mounting the flexible strip on asubstrate, and providing a mounting structure for retaining opticalcircuit boards on the backplane adjacent to said waveguide ends.

In one embodiment, the flexible strip is fabricated by forming asacrificial layer on a temporary substrate, depositing a first claddinglayer on the sacrificial layer, depositing a first core layer on saidcladding layer, forming a first core pattern from said core layer,depositing a second cladding layer over the first core pattern andexposed portions of the first cladding, removing the sacrificial layerand temporary substrate, depositing a second core layer and forming asecond core pattern from said second core layer on the first claddinglayer opposite the first core pattern, and depositing a third claddinglayer on the formed second core pattern and exposed portions of thefirst cladding.

In another embodiment, the forming of the flexible strip includesforming a bottom waveguide layer including a bottom cladding layer,forming a top waveguide layer including a top cladding layer, andjoining the top cladding layer to the bottom cladding layer.

An object of the present invention is to provide an flexible opticalconnector which may be used in an optical backplane, and a method offorming an optical backplane that are less expensive that prior artoptical backplanes and methods of fabricating optical backplanes.

Another object of the present invention to provide an optical backplanethat is manufactured separately from either a support substrate or fromcircuit board brackets.

A further object of the present invention to provide an opticalbackplane that allows for electrical and optical connections along thesame edge of an optical circuit board.

Yet another aspect of the present invention to provide a waveguidestructure that is attached to form an optical backplane at the ends ofthe waveguide.

These features, together with the various ancillary provisions andfeatures which will become apparent to those skilled in the art from thefollowing detailed description, are attained by the flexible opticalbackplane and method of the present invention, preferred embodimentsthereof being shown with reference to the accompanying drawings, by wayof example only.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing aspects and the attendant advantages of this inventionwill become more readily apparent by reference to the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

FIGS. 1A and 1B depict exemplary optical circuit boards for use with theoptical backplane of the present invention;

FIG. 2 is a perspective view of an embodiment of an optical interconnectof the present invention used as an optical backplane, showing opticaland electrical connections on a backplane;

FIG. 3 is a cross-sectional of the optical backplane of FIG. 2 alongview lines 3-3;

FIGS. 4A-4H illustrate a method for manufacturing an opticalinterconnect of the present invention; and

FIGS. 5A-5H illustrate an alternative method for manufacturing anoptical interconnect of the present invention.

FIGS. 6A-6F illustrate another alternative embodiment for manufacturingan optical interconnect of the present invention.

Reference symbols are used in the Figures to indicate certaincomponents, aspects or features shown therein, with reference symbolscommon to more than one Figure indicating like components, aspects orfeatures shown therein.

DETAILED DESCRIPTION

The present invention is directed to flexible optical interconnectstructures, and methods of manufacture, which are for particularlysuitable for connecting optical circuit boards on a common opticalbackplane. The transition from electrical to optical interconnection ofhigh speed electronic devices is inevitable with the increasedoperational frequencies of integrated circuits (“ICs”) and other circuitstructures. Unlike electrical interconnect structures, opticalinterconnect structures are free of capacitive loading and do not sufferfrom cross-coupling between channels. Optical interconnects are,therefore, much faster than electrical connection, and allow reducedpitch between adjacent signal channels.

Exemplary optical circuit boards A, which can be connected to theoptical backplane of the present invention, are shown in FIGS. 1A and1B. FIG. 1A shows a first exemplary optical circuit board A whichincludes several components C, such as IC “chips” that incorporate oneor more optical, electronic and electro-optical components, such assemiconductor lasers, such as Vertical Cavity Surface Emitting Lasers(VCSEL) and edge emitting lasers, photodiodes (PD), traditionalelectronic circuitry or other optical or electronic components. In oneaspect, the present invention is directed to backplane for acceptingoptical circuit boards, such as board A, to provide power to the boardand to route electrical and optical signals between such boards, andother components.

Exemplary optical circuit board A (alternatively referred to herein as“circuit board” or “board”) is layered, and includes one or more layershaving conductive traces T for routing electronic signals and one ormore layers having waveguides W for routing optical signals. Some oftraces T and waveguides W are patterned to route signals betweencomponents C and others are patterned to terminate at an edge EA toallow for electrical and optical connections to other boards or devices.As shown in FIG. 1A, traces T terminate within a region E of edge EA,and waveguides W terminate within a region O of the edge.

Exemplary optical circuit board A′ of FIG. 1B is generally similar tooptical circuit board A of FIG. 1A, but contains only electrical wiring.In FIG. 1B edge EA′ comprises an edge-mounted electro-optic device, suchas an LED or a laser, that projects light L in the direction of regionO, adjacent to the edge of the board.

An exemplary embodiment of one aspect of the present invention is shownin FIGS. 2 and 3. FIG. 2 shows a backplane 100 comprising a substrate101 with an optical backplane 110 and an electrical backplane 120mounted or formed thereon. FIG. 3 is a cross-sectional view of thebackplane 100 of FIG. 2 along view lines 3-3. As shown in FIG. 3, in oneembodiment, optical backplane 110 may be positioned on substrate 101 byalignment standoffs 304 and secured with adhesive 306. Optical backplane110 includes waveguides 113, 115, and 117, and electrical backplane 120includes electrical traces 127. Exemplary backplane 100 has one or moremounting structures for retaining circuit boards in a position thatallows for the exchange of electrical and optical signals between thecircuit boards and backplane 100. In FIG. 2, the mounting structurecomprises two sets of bracket pairs 131 a, 131 b and 133 a, 133 b.Bracket pairs 131, 133 include electrical connector brackets 131 b, 133b and optical connector brackets 131 a, 133 b. Preferably, the mountingstructure permits removal of the circuit boards without damage to eitherthe circuit boards or to the substrate. While the embodiment of FIG. 2has brackets for receiving two circuit boards, those skilled in the artwill appreciate that the mounting structure can be constructed to retainmore than two circuit boards on the backplane. Likewise, while theexemplary mounting structure comprises bracket pairs, other structuresmay be used to position and removably retain circuit boards on thebackplane. Moreover, the circuit boards and backplane may be configuredso that only optical connections are made on the backplane.

In the exemplary embodiment of FIGS. 2 and 3, one or more photonicdevices, such as lasers or light emitting diodes LEDs for transmittinglight or photodiodes PDs for receiving light are mounted on the edges ofoptical circuit boards A and B. Alternatively, the board edges may havewaveguide ends which transmit light to or from semiconductor lasers,LEDs, PDs, or other photonic devices mounted on or formed within thecircuit boards. In either case, when the boards are mounted on thebackplane, the photonic devices or the waveguide ends are positionedadjacent to waveguide ends on optical substrate 110 such that opticalsignals may be transmitted therebetween.

Electrical connector brackets 131 b and 133 b provide contact betweenelectrical traces on the optical circuit boards and electrical traces127 of electrical backplane 120. Suitable structures for providingelectrical contact are well known and need not be described in detail.

As noted, optical backplane 110 comprises a plurality of waveguides thathave ends adjacent to the optical circuit boards for making opticalconnections therebetween. Thus, for example, waveguides 113, 115, and117, each have one end near optical circuit board A and another end nearoptical circuit board B, to provide a plurality of optical paths forinterconnecting the optical circuit boards. For simplicity, only threesuch optical paths are shown. Preferably, optical backplane 110 isflexible, with the optical layers formed from optical polymers, and isattached to substrate 101.

As an illustrative example of the three-dimensional routing of lightthrough optical backplane 110, waveguides 113, 115, and 117, definingthree light paths, are shown as having waveguide ends 113A, 115A, and117A, respectively, adjacent to an edge of optical circuit board A, andwaveguide ends 113B, 115B, and 117B, respectively, adjacent to an edgeof optical circuit board B, to provide transmission of optical signalsbetween the optical circuit boards. For exemplary purposes, thedirection of propagation of optical signals to and from optical circuitboard A are shown as rays A1, A2, and A3, and those to and from opticalcircuit board B are shown as rays B1, B2, and B3. Each waveguide endpreferably includes a lens for focusing the light entering or leavingthe optical backplane. Thus, for example, in the embodiment shown inFIG. 3, a lens 302 is positioned at each waveguide end, 113A, 113B. Theends of the waveguides in optical substrate 110 serve as the input andoutput ports of the waveguides. While lenses 302 are shown positioned atthe waveguide ends in FIG. 3, in other embodiments lens may bepositioned anywhere between the waveguide end and the light transmitteror receiver.

As depicted in FIG. 3, the optical connector of the present inventioncontains a plurality of waveguide layers such that the optical signalsmay cross within the backplane. This allows complex signal routingbetween any two points on optical circuit board A and optical circuitboard B.

Propagation of light through optical backplane 110 is illustrated inFIG. 2. A light signal is transmitted from optical circuit board A asray A2 into waveguide end or input port 117A, where it propagates alongwaveguide 117 to waveguide end 117B, and is received by optical circuitboard B as ray B2. For simplicity the optical path of waveguide 117follows a straight line. However, as depicted in FIG. 3, optical path117 alternately runs in two different waveguide layers to enable otheroptical paths to cross it. As shown in FIG. 2, a second light signal isalso transmitted from circuit board A as ray A2 into waveguide end 115A,where it propagates along waveguide 115 to waveguide end 115B, and isreceived by optical circuit board B as ray B2, and a third light signalis transmitted from optical circuit board B as ray B1 into waveguide end113B, where it propagates along waveguide 113 to waveguide end 113A, andis received by optical circuit board A as ray A3.

Thus, in FIGS. 2 and 3, optical paths or waveguides 113, 115, and 117include various straight sections in multiple waveguide layers in theoptical backplane 110, pass-through structures that direct light fromone layer to another, and turning elements that direct light to and fromthe input and output ports at the ends of their respective paths. Inthis manner, the optical paths may cross over or under each other, andlight can be directed into and out of the backplane in a direction whichis perpendicular to the backplane.

FIG. 3 shows exemplary optical backplane 110 having a top waveguidelayer 301, comprising patterned core material 307 a and cladding layer309 a, and a bottom waveguide layer 305 comprising patterned corematerial 307 b and cladding layer 309 b, separated by a middle claddinglayer 303. Although two waveguide layers are shown for simplicity, morethan two waveguide layers may be included in the flexible connector ofthe present invention. Two waveguide layers is the minimum needed toallow light paths to cross according to the present invention, andshould be sufficient for most applications.

In the illustrated embodiment light passing in the longitudinaldirection in optical backplane 110, i.e., in the direction between thewaveguide ends, generally travels through bottom waveguide layer 305,except at the places where it is necessary to cross another opticalpath, and light passing in the optical backplane transverse to thelongitudinal directions is generally travels through upper waveguidelayer 301. Waveguide layers 301 and 305 each includes a waveguide core307, a waveguide cladding 309, and angled sections 311. Angled sections311 are preferably angled 45° relative to the optical backplane and havea metallic or other suitable coating to provide good light reflectance.

As an example, the optical path through waveguide 115 is as follows.Light from LED of optical circuit board A is focused by lens 302 onwaveguide end 115A into the surface of optical backplane 110 and intowaveguide end portion 313. A combination of straight and angled sections311 route light along the waveguide in optical backplane 110. Asnecessary to cross another light path, light in one waveguide layer isredirected to the another waveguide layer. Thus, in FIG. 3, light isredirected from the bottom waveguide layer 305 by pass-through 315through cladding layer 303 and redirected by another angled section 311into the top waveguide layer 301. Preferably the pass-throughs areformed from the waveguide core material. After traveling the length ofwaveguide 115, the light is emitted into lens 302 on waveguide end 115Band focused onto PD of optical circuit board B. Waveguides 113 and 117are formed in the same manner as waveguide 115. In one embodiment, thewaveguides provide for routing signals in the direction between theoptical circuit boards in one layer, and light in an orthogonaldirections in another level.

While FIG. 3 depicts the use of angled surfaces to redirect light withinthe optical backplane of the present invention, in an alternativeembodiment, the light is redirected by curved waveguides. Curvedwaveguides are used in the same general configuration as the lateral 45°mirrors shown in FIG. 2 for redirecting the light by 90°, or any otherselected angle. Instead of abruptly turning the light by using anangled, reflective surface, the waveguide can be continuously curved topoint perpendicular to the original propagation direction. Moregenerally, by using a desired curvature, the propagation direction oflight in the waveguide can be redirected by any angle relative to theoriginal propagation direction. Those skilled in the art will appreciatethat there is a limit to the radius of curvature of a curved waveguidewhich is a function of the indices of refraction of the core andcladding materials at the operating light wavelength. Thus, the radiusof the waveguide curvature depends on the waveguide refractive indexes,waveguide dimensions, light wavelength etc. A preferable waveguideradius of curvature is from 1 to 10 mm. However it can be smaller andlarger depending on the above parameters.

A sequence of steps associated with one method of manufacturing aflexible optical connector of the present invention is illustrated inFIGS. 4A-4H. FIG. 4A shows a sacrificial layer 403, a first claddinglayer 303, and a bottom waveguide core material 405 sequentiallydeposited on a temporary substrate 401. Temporary substrate 401 may beany suitable substrate material, such as silicon, ceramic, glass, orplastic.

The waveguide structures, specifically the cores, claddings andpass-throughs (which may also be referred to as “optical vias”), arepreferably formed from flexible optical materials having sufficientstrength to allow for the manufacturing processes describedsubsequently. Preferred waveguide core and cladding materials includeoptical polymers such as optical polyimides (OPI), optical epoxy resins,and other optical polymers. Appropriate optical polymers are well-knownin the art, and need not be described in detail. Optical polymers ingeneral and OPI films in specific can be used to form highly transparentwaveguides that are directly or indirectly patterned using well-knownphotolithographic techniques. Optical polymers are preferred becausethey are flexible, relatively rugged, inexpensive and generally easy towork with. Generally, optical polymers are deposited by applying auniformly thick liquid layer and then hardening it by curing, such as bythe application of heat or UV radiation. The techniques for depositingand curing optical polymeric layers are well known and need not bedescribed in detail.

First cladding layer 303 is preferably about 5 to about 50 μm thick.Core material 405 has a refractive index suitably higher than that ofthe cladding and is preferably about 5 to about 100 μm thick.Sacrificial layer 403 may be any suitable material, such as a metal,such as copper or tungsten, or an oxide, such as silicon dioxide, thatcan facilitate the separation of substrate 401 from the resultingwaveguide structure.

FIG. 4B shows the formation of a first patterned core structure 410 frombottom waveguide core material 405 by photolithography of the core layerand etching to define the shapes of the optical waveguide. As previouslydescribed, the waveguide may have a planar surface 407 and angledsections 311. Angled sections 311 can be formed, for example, by laserablation, gray scale masking, dicing using an angled blade, and may becoated with a very thin reflective film, such as gold, silver oraluminum, to form reflective surfaces, preferably at an angle of 45°.Any suitable metal deposition technique, such as sputtering,evaporation, MOCVD or the like, may be used to form the reflectivecoatings.

As shown in FIG. 4C, the next step is the deposition of second cladding309 on first core pattern 410. It will be observed that in the exposedareas, ie., those areas where the core material 405 has been removed,the second cladding 309 is deposited directly on the first cladding 303.As depicted, the upper surface of second cladding layer 309 ispreferably planar such that the combination of second cladding layer 309and core pattern 410 is substantially uniformly thick.

Next, as shown in FIG. 4D, second cladding 309 and core 410, which makeup first waveguide layer 305, and first cladding layer 303 are separatedfrom substrate 301. Separation is facilitated by sacrificial layer 403,which may be selected to allow chemical etching or easy peeling.

As shown in FIG. 4E, after the substrate and sacrificial layers havebeen removed, the remaining structure is flipped over and an opening 408is formed in cladding layer 303 to allow fabrication of an opticalpass-through between waveguide layers. Thereafter, a second waveguidecore material 409 is deposited over cladding layer 303 and opening 408.Waveguide core material is preferably from about 5 to about 100 μmthick.

FIG. 4F shows the formation of a second patterned core 420 from topwaveguide core material 409. In the example depicted in FIGS. 4F-4H, thesecond patterned core has a first section which runs parallel to thecross-sectional plane and a second section which runs perpendicular tothe cross-sectional plane. These structure may be fabricated in the samemanner previously described in connection with FIG. 4B, e.g., usingphotolithography, etc.

As shown in FIG. 4G, top waveguide layer 301 is then formed by thedeposition of cladding 309 on second patterned core 420, and a flexiblesupport 415 is added to bottom waveguide layer 305. Flexible support 415may be formed of any suitable material, such as a flexible KAPTON® filmor any other non-optical polyimide film having suitable properties, suchas durability, strength, low cost, etc. Flexible support 415 may begrown or deposited onto the waveguide structure, or may be separatelyformed and attached using an adhesive layer.

Lastly, as shown in FIG. 4H, the waveguide structures may be diced andpolished, if necessary, to form optical backplane 110. Preferably, theoverall thickness of the flexible connector of the present invention isfrom 50 to 2,000 μm.

An alternative method of manufacturing a flexible connector suitable foruse in optical backplane 110 is now described. First a bottom waveguidelayer 305 and cladding layer 303 are formed as illustrated and asdiscussed in reference to FIGS. 4A-4D. Next, a similar process is usedto separately form the top waveguide layer. Specifically, as shown inFIG. 5A, sacrificial layer 403, cladding layer 303, and top waveguidecore material 405 are sequentially deposited on a substrate 401, and thecore material is patterned.

FIGS. 5B-5D, which are similar to the steps of FIGS. 4E-4F depict thesteps used to form a top waveguide layer 301 on a cladding layer 303. Asshown in FIG. 5E, the bottom waveguide layer 305 of FIG. 4D and topwaveguide layer 301 of FIG. 5D are aligned with facing cladding layers303 and joined together. Any suitable means for joining the two layersmay be used, for example, an adhesive 501 may be applied betweencladding layers 303 to fix the positions of the aligned top waveguidelayer 301 and bottom waveguide layer 305.

Thereafter, as shown in FIG. 5G, the resulting structure may diced andpolished, if necessary, and a flexible support 415 is added to bottomwaveguide layer 305 to form optical backplane 110.

FIGS. 6A-6F illustrate yet another process for manufacturing theflexible optical interconnect of the present invention. FIG. 6A shows asubstrate 601 of any suitable material. In one embodiment, substrate 601is a flexible polyimide film. Depending on the design and use of theoptical interconnect, it may be desirable to use a temporary substrate,as in the previously described embodiments, in which case an optionalsacrificial layer (not shown in FIG. 6) may be formed between substrate601 and lower or first cladding layer 603. A “wedge” layer 605 is thendeposited on lower cladding layer 603 and patterned, as described above,to create structures 605 a having a plurality of angled surfaces as showin FIG. 6B. Preferably, the angled surfaces are formed in pairs (onesuch pair is shown in FIGS. 6B-6F) with the members of each pair beingin an opposing relationship. The angled surfaces are preferably coatedwith a reflective material, as previously described and are preferablyat an angle of 45° to the plane defined by substrate 601.

As shown in FIG. 6C a first core layer 610 is then deposited over thepatterned wedge layer 605. Core layer 610 is preferably an opticalpolymer having good planarization properties. The “tops” of “wedge”structures 605a are, preferably, kept as small as practical tofacilitate planarization of first core layer 610. As depicted in FIG.6D, a first patterned core layer 610 a is formed within the area definedby wedge structures 605 a. A second cladding layer 615 is formed overthe entire structure and planarized. A second core layer is then formedover top cladding 615, and is patterned to form second core structure620 and a vertical optical via 625, as shown in FIG. 6E. Second corestructure 620 includes complementary angled surfaces, as depicted,having a reflective film deposited thereon. An upper or third claddinglayer 630 is then deposited over the upper surface of the resultingstructure, and is planarized to provide a flat surface leaving the upperend of vertical optical via 625 exposed, as shown in FIG. 6F. Additionallayers may be added using any of the techniques described herein, ormultiple structures of the kind depicted in FIG. 6F may be joinedtogether. Likewise, substrate 601 may be removed and a different oradditional flexible backing material may be added.

In operation, as will be appreciated by those skilled in the art, theangled surfaces of the first and second core layers redirect lightbetween the layer, thereby enabling complex routing of light signalsthrough the flexible optical interconnect. Specifically, thisarrangement allows light paths to cross over each other, so that lightcan be directed through the optical interconnect in two directions.Preferably, light in one layer travels in one direction in an arbitraryx-y plane defined by the substrate, while light in the second layertravels in the orthogonal direction.

Many alternative embodiments are within the scope of the presentinvention, including, for example, optical backplane waveguides may haveends near only one of the connectors to provide optical communicationoff of the optical backplane, and waveguides that include beam splittersto allow an optical signal to communicate with more than one receivedoptical circuit board.

1. An optical connector, comprising: a flexible strip having a pluralityof optical waveguides formed in a plurality of waveguide layers forproviding a plurality of optical paths between opposing ends of saidflexible strip, at least one of said optical paths running through atleast two waveguide layers.
 2. The optical connector of claim 1, whereinsaid flexible strip further comprises at least one pass-through betweenwaveguide layers such that at least one of said optical paths is routedthrough at least two waveguide layers.
 3. The optical connector of claim2, wherein said at least one pass-through includes a complementary pairof reflective angled surfaces, one of said pair being positioned in eachof said two waveguide layers, for redirecting light between said twowaveguide layers.
 4. The optical connector of claim 1, wherein saidwaveguide has a thickness of from about 50 to about 1000 μm.
 5. Abackplane structure comprising the optical connector of claim 1 mountedon a backplane substrate and further comprising a mounting structure forpositioning and retaining at least two optical circuit board adjacent torespective ends of said flexible strip to provide a plurality of opticalpaths for communicating optical signals between the optical circuitboards.
 6. The backplane of claim 5 further comprises a plurality ofelectrical traces for communicating electrical signals between saidoptical circuit boards.
 7. The backplane of claim 5 wherein at least twoof said optical paths within said flexible strip cross over.
 8. Anoptical backplane adapted to accept a plurality of optical circuitboards and optically connect one or more optically active areas of saidaccepted optical circuit boards, comprising: a substrate; a mountingstructure for retaining and positioning the optical circuit boards onsaid substrate; and an optical interconnect structure having a pluralityof waveguides formed in a plurality of waveguide layers, each waveguidehaving a pair of waveguide ends defining a light path therebetween forcommunicating light signals between said optical circuit boards.
 9. Theoptical backplane of claim 8, wherein at least two of said waveguidepaths cross.
 10. The optical backplane of claim 9, wherein said opticalinterconnect structure comprises a flexible strip mounted on saidsubstrate.
 11. The optical backplane of claim 10 wherein said flexiblestrip comprises a plurality of waveguide layers and at least onepass-through for redirecting light traveling in one of said waveguidelayers to another of said waveguide layers.
 12. The optical backplane ofclaim 11 wherein said pass-through comprises a complementary pair ofangled reflective surfaces.
 13. The optical backplane of claim 10,wherein said flexible strip has a thickness of from about 50 to about1000 μm.
 14. The optical backplane of claim 8 wherein said mountingstructure comprises a plurality of bracket pairs.
 15. An opticalbackplane, comprising: a substrate; a mounting structure for removablyretaining and positioning a plurality of optical circuit boards; aflexible strip mounted on said substrate, said flexible strip comprisinga plurality of waveguide layers having a plurality of optical pathsformed therein, each of said optical paths having an input port forreceiving light from one of the optical circuit boards and an outputport for transmitting light to another of the optical circuit boards.16. The optical backplane of claim 15, said flexible strip furthercomprising at least one cladding layer separating adjacent waveguidelayers, and where at least one of said optical paths includes portionswithin at least two of said plurality of waveguide layers.
 17. Theoptical backplane of claim 16, wherein said waveguide further includesat least one pass-through between said two waveguide layers.
 18. Theoptical backplane of claim 17, wherein said at least one pass-throughincludes a complementary pair of angled reflective surfaces forredirecting light from one of said waveguide layers to another of saidwaveguide layers.
 19. The optical backplane of claim 18 wherein at leasttwo of said optical paths cross over each other.
 20. The opticalbackplane of claim 15, wherein said flexible strip has a thickness offrom about 50 to about 1000 μm.
 21. The optical backplane of claim 15wherein said waveguide layers are formed from an optically transparentpolymer.
 22. The optical backplane of claim 21 wherein said opticallytransparent polymer is a polyimide.
 23. A method of forming an opticalbackplane for optically connecting a plurality of optical circuitboards, comprising: forming a flexible strip comprising a plurality ofoptical paths formed in a plurality of waveguide layers; mounting saidflexible strip on a substrate; and attaching a mounting structure onsaid substrate for removably retaining and positioning optical circuitboards in a location adjacent to the ends of said optical paths.
 24. Amethod of forming a flexible optical interconnect structure, comprising:forming a sacrificial layer on a temporary substrate; depositing a firstcladding layer on said sacrificial layer; forming a core layer on thetop of said cladding layer; forming a first core pattern on saidcladding layer from said core layer such that a portion of the top ofsaid first cladding layer is exposed; depositing a second cladding onsaid first core pattern and exposed portion of said first cladding;removing said sacrificial layer and said temporary substrate to exposethe bottom of said first cladding layer; forming a second core layer onthe bottom of said first cladding layer; forming a second core patternfrom said second core layer such that a portion of the such that aportion of the bottom of said first cladding layer is exposed; anddepositing a third cladding on said second core pattern and exposedportion of said first cladding.
 25. The method of claim 24 furthercomprising mounting the resulting structure on a flexible support. 26.The method of claim 24 wherein said core and cladding layers are formedfrom optical polymers.
 27. The method of claim 24 wherein at least oneof said core patterns includes an angled surface.
 28. The method ofclaim 27 wherein said angled surface is coated with a reflective layer.29. A method of forming a flexible optical interconnect, comprising:forming a bottom waveguide layer comprising a first light path andincluding a bottom cladding layer; separately forming a top waveguidelayer comprising a second light path and including a top cladding layer;and thereafter joining said top cladding layer to said bottom claddinglayer.
 30. The method of claim 29 wherein said top and bottom waveguidelayers have complementary pass-through structures formed therein, suchthat when said layers are joined together light traveling in said firstwaveguide layer will be redirected by said complementary pass-throughstructures into said second light path.
 31. A method of forming aflexible optical interconnect, comprising: forming a first claddinglayer over a flexible polymer substrate; forming patterned structureover said lower cladding layer, said patterned structure having aplurality of angled surfaces, at least two of said angled surfaces beingin an opposing relationship; forming a first patterned core layer in thearea between said at least two angled surfaces; forming a secondcladding layer over said first core layer; forming a second patternedcore layer over said second cladding layer, said second patterned corelayer having at least one angled surface for redirecting between saidfirst and second patterned core layers; forming a third cladding layerover said second patterned core layer.
 32. The method of claim 31,further comprising forming at least one vertical optical via in saidinterconnect structure for directing light into or out of the structurein a direction which is orthogonal to the plane defined by saidsubstrate.
 33. The method of claim 31 further comprising the step ofdepositing a reflective material on said angled surfaces.
 34. The methodof claim 31 wherein each of said layers comprises a polymer.